Conventional adjustable metal shelving commonly includes set screws for anchoring the shelves at selected elevations. The screws are turned until they tightly engage the metal corner posts. Overtightening of the screws could damage the posts or, in some cases, strip the threads of the screw. On the other hand, should the screws be too loose, or should they become loosened during use, the stability of the entire structure could be affected and the equipment or articles supported by the loosened shelf could fall and become damaged. Furthermore, the set screw arrangement, while offering an advantage of infinite adjustability, also has the disadvantage of providing little or no indication of just when a shelf is level, thereby presenting a real possibility that such a shelf might be tightened while in a slightly tipped condition, with consequential effects on the alignment and stability of the assembly as a whole.
U.S. Pat. Nos. 3,280,767 and 3,344,756 illustrate constructions in which set screws directly engage the corner posts to hold the shelves in position. A modified construction, in which a set screw is used but does not directly engage the post, is disclosed in U.S. Pat. No. 3,747,540. U.S. Pat. Nos. 3,424,111, 3,523,508 and 3,757,705 teach constructions in which set screws are eliminated and the shelves are held in place upon circumferentially grooved posts by sleeves equipped with portions receivable in the grooves. Co-owned U.S. Pat. No. 3,589,746 teaches a system in which the shelves are locked in place with friction corner braces. While the constructions of the latter four patents all provide good stability and load support strength, such advantages are offset at least in part by their relative complexity and the absence of smooth uninterrupted surfaces that could simplify manufacture and facilitate cleaning and maintenance.